One common method for printing images on a receiver material is referred to as electrophotography. The production of black-and-white or color images using electrophotography generally includes the producing a latent electrostatic image by uniformly charging a dielectric member such as a photoconductive substance, and then discharging selected areas of the uniform charge to yield an imagewise electrostatic charge pattern. Such discharge is generally accomplished by exposing the uniformly charged dielectric member to actinic radiation provided by selectively activating particular light sources in an LED array or a laser device directed at the dielectric member. After the imagewise charge pattern is formed, it is “developed” into a visible image using pigmented or non-pigmented marking particles (generally referred to as “toner particles”) by either using the charge area development (CAD) or the discharge area development (DAD) method that have an opposite charge to the dielectric member and are brought into the vicinity of the dielectric member so as to be attracted to the imagewise charge pattern.
Thereafter, a suitable receiver material (for example, a cut sheet of plain bond paper) is brought into juxtaposition with the toner image developed with the toner particles in accordance with the imagewise charge pattern on the dielectric member, either directly or using an intermediate transfer member. A suitable electric field is applied to transfer the toner particles to the receiver material in the imagewise pattern to form the desired print image on the receiver material. The receiver material is then removed from its operative association with the dielectric member and subjected to suitable heat or pressure or both heat and pressure to permanently fix (also known as fusing) the toner image (containing toner particles) to form the desired image on the receiver material.
Plural toner particle images of, for example, different color toner particles respectively, can be overlaid with multiple toner transfers to the receiver material, followed by fixing of all toner particles to form a multi-color image in the receiver material. Toners that are used in this fashion to prepare multi-color images are generally Cyan (C), Magenta (M), Yellow (Y), and Black (K) toners containing appropriate dyes or pigments to provide the desired colors or tones.
It is also known to use special spot toners to provide additional colors that cannot be obtained by simply mixing the four “primary” toners. An example is a specially designed toner that provides a color spot or pearlescent effect.
With the improved print image quality that is achieved with the more recent electrophotographic technology, print providers and customers alike have been looking for ways to expand the use of images prepared using electrophotography. Printing processes serve not only to reproduce and transmit objective information but also to convey esthetic impressions, for example, for glossy books or pictorial advertizing.
The desire to provide fluorescing effects has existed for several decades and U.S. Pat. No. 3,713,861 (Sharp et al.) describes coating a fluorescent material over a document image.
Many color images cannot be reproduced using the traditional CYMK color toners. Specifically, fluorescing colors or tones cannot be readily reproduced using the CYMK color toner set. It has been proposed to incorporate fluorescing pigments or dyes into liquid toner particles as described in U.S. Pat. No. 5,105,451 (Lubinsky et al.).
U.S. Patent Application Publication 2010/0164218 (Schulze-Hagenest et al.) describes the use of substantially clear (colorless) fluorescent toner particles in printing methods over color toner images. Such clear fluorescent toner particles can be used for security purposes since they are not colored except when excited with appropriate light. Other invisible fluorescent pigments for toner images are described in U.S. Pat. No. 6,664,017 (Patel et al.).
Printing processes for providing one or more color toner images are known, but it is also desired that fluorescing effects can also be provided for any type of color toner image in order to expand the color gamut while using conventional non-fluorescing color toners. However, it has been difficult to properly design desired fluorescing effects using known fluorescing colorants (dyes and pigments) as many of them are very sensitive to the illuminating radiation.
In addition, some fluorescing colorants are difficult to disperse within various polymeric binders that are used to prepare dry toner particles. The fluorescing colorants could also adversely affect the charging properties of the toner particles. For example, many of the fluorescing colorants are positive-charging and therefore it is very difficult to prepare negative-charging toners using such fluorescing colorants. Furthermore, most of the fluorescing colorants exhibit undesirable solubility in hot silicone fuser oils used during the fixing (fusing) steps of the printing process. This can lead to coloration of the entire image even where no color toner is applied, because the hot fusing oil is absorbed and carried throughout the apparatus by the receiver materials. All of these shortcomings can diminish the effects intended from use of the fluorescing colorants.
There is a need to expand the possible color gamut with fluorescing effects without the noted problems.